Natural gas at the outlet of production wells is often associated with formation water containing dissolved salts (sodium chlorides, potassium chlorides, calcium chlorides, sodium bicarbonates, etc.). The natural gas is transported from the production site to a processing site by circulation in lines. If the natural gas is water-saturated and at equilibrium with an aqueous phase, depending on the transportation conditions (pressure and temperature), hydrate plugs are likely to form which may lead to production stop. To avoid such problems, a hydrate inhibitor such as glycol is injected into the pipelines. An aqueous solution containing between 60% and 90% by weight of glycol can be used. After transportation, a mixture consisting of formation water and glycol is recovered, then processed in a glycol regeneration plant in order to reconcentrate the glycol, i.e. to remove the water. The regenerated glycol can again be injected into the pipelines carrying the natural gas.
Glycol distillation systems for separating the glycol from the water-glycol mixture are known to the man skilled in the art. In general, the systems of the prior art allow to obtain an aqueous solution containing between 70% and 90% glycol.
However, regeneration of the glycol leads to concentrate the salts, initially present in the formation water, in the regenerated glycol. Salt concentration is the cause of operating problems such as salt accumulation on certain parts of the regeneration device, thus reducing the efficiency thereof, and such as corrosion of the regeneration device.
The present invention provides a method of regenerating an aqueous glycol solution allowing to remove part of the water, as well as the salts.
The solubility of the salts in aqueous glycol solutions varies with the temperature and the water content of the solution. Adjusting the temperature and lowering the water content allows the solubility of the salts in aqueous glycol solutions to be reduced. It is thus possible to cause precipitation of the salts, the precipitated salts being then separated from the aqueous glycol solution.